1. Field of the Invention
The invention relates to communication system and, more particularly, to a method and apparatus for adjusting reference frequency of communication system.
2. Description of the Prior Art
Frequency division multiplexing transmission technology is mostly used for modern wireless communication system, and its principle is to divide usable bandwidth into numbers of frequency bands to enable the data to be parallelly transmitted via those frequency bands to promote data transmission rate.
The radio waves will be influenced by the terrain or the surface features during transmission in air, and some phenomena which lower the quality of signal are generated, such as refraction, diffraction, interference, multipath fading and so on. However, those problems can be avoided by utilizing orthogonal frequency division multiplexing (OFDM). Besides, the OFDM is capable of high data transmission rate, high bandwidth utility rate and avoiding multipath fading and thereby is generally applied to modern wireless communication system.
However, since the frequency band is divided into numbers of sub-channels, the sensitivity of signal with frequency is substantially improved. Consequently, in the OFDM wireless communication system, it becomes a critical issue to perform frequency recovery with received signal based on accurate reference frequency and further read the data accurately in the signal.
In traditions, in order to recover a shifted reference frequency caused by noises in the OFDM wireless communication system, a pseudo-noise sequence usually is used for estimating shifted amount of a reference frequency. However, the calculation of estimating shifted amount of the reference frequency used by this method is very huge. Moreover, due to the influence of selectively fading at some sub-channels, the shifted amount estimation of the reference frequency will be incorrect, and thereby calibration of the reference frequency will be hard to proceed.
Accordingly, the main goal of the invention is to provide a method and apparatus for adjusting reference frequency of the wireless communication receiving terminal, so as to solve the aforesaid problems.